Large sections of central Frankfurt, Germany were evacuated on Sunday in preparation for authorities to defuse a World War II-era, 1.4-ton HC 4000 air mine, with CNN reporting at least 60,000 people were asked to leave the area while the bomb defusal operation proceeds.

Take a big sigh of relief and wipe that bead of sweat off your brow: The bomb was successfully defused, but still needs to be removed from the area with utmost caution, according to Deutsche Welle.

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The air mine, one of the largest varieties of ordnance used during the war, is of a type sometimes referred to as a blockbuster due to its ability to destroy entire rows of buildings. It was presumably dropped during the 1939-1945 air war the Allies waged on Nazi Germany, and was only discovered during recent construction work after sitting underground for at least 72 years.

“This bomb has more than 1.4 tonnes of explosives,” Frankfurt fire department chief Reinhard Ries said, according to ABC News. “It’s not just fragments that are the problem, but also the pressure that it creates that would dismantle all the buildings in a 100-metre radius.”

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According to the BBC, the evacuation zone contained “20 retirement homes, an opera house, and Germany’s central bank where half the country’s gold reserves are stored.”

“We want to avoid not being able to return to these buildings on Monday morning,” Ries added. “That would create a very difficult situation for Frankfurt.”

Experts estimate thousands of tons of explosives from World War II-era saturation bombing still remain scattered around Germany, holdouts from the estimated 2.7 million tons of bombs Allied air forces dropped to eviscerate Nazi military and industrial capacity. According to Smithsonian, authorities discover approximately 2,000 tons of explosives a year, and from 2000-2016, 11 bomb technicians were killed in failed defusal attempts.

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Just the day before, authorities evacuated 20,000 in preparation to defuse a US-made bomb in the city of Koblenz.

One town, Oranienburg, hosted Nazi chemical facilities, aircraft manufacturing plants, railway junctions and an S.S. arms depot, according to Deutsche Welle, leading the Allies to drop more than 10,000 bombs on the area. Technical University of Cottbus bomb expert Wolfgang Spyra told the news agency he estimated seven to 15 percent of the bombs were duds, meaning hundreds still laid under the town.

Explosives used in World War II-era Allied ordnance were generally stable enough to remain dangerous for long amounts of time, though other components of the bombs often degrade, making them particularly hazardous to try and defuse.

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“The scale of this bomb is overwhelming,” Ries said, per CNN. “I have never seen anything like it.”